Electrical contact compositions and novel manufacturing method

Abstract

A new class of low chop contact materials based on Ag-chromium carbide and Ag-Cr compositions have an essentially 100% dense, porosity free microstructure. These materials combine the advantageous properties of Ag-WC and Cu-Cr contacts without their disadvantages. A method of making this new class of low chop contact materials includes the steps of cold pressing a mixture of Ag and chromium or chromium carbide to form an unsintered blank and the elevated temperature infiltration of silver into the unsintered blank to obtain an essentially 100% dense, porosity free microstructure.

We claim: 
     
       1. An improved electrical contact comprising an alloy of Ag and a material selected from the group consisting of Cr 3  C 2 , Cr 7  C 3 , Cr 23  C 6 , mixtures thereof and Cr wherein about 0.10 to 0.99% by weight of a ternary element is selected from the group consisting of bismuth, tellurium, thallium and said ternary element is added to said alloy to enhance an arc sustaining vapor. 
     
     
       2. The contact of claim 1, wherein about 0.5 to 2.5% by weight of cobalt is added to said electrical composition to improve its wetting properties and enhance an essentially 100% dense, porosity tree microstructure of said contact. 
     
     
       3. The contact of claim 2, wherein the alloy comprises about 50 to 60% by weight Ag and about 40 to 50% by weight Cr 3  C 2 . 
     
     
       4. The contact of claim 3, wherein the alloy comprises about 58% by weight Ag and about 42% by weight Cr 3  C 2 . 
     
     
       5. The contact of claim 1, having an essentially 100% dense, porosity free microstructure derived from elevated temperature infiltration of said silver into said composition.